Benefit agents, such as perfumes, enzymes and the like are often delivered to a substrate in the form of a droplet or particle. Such delivery can be achieved by using a liquid droplet which can exist within another liquid or within the air, such as an aerosol for example. Another method is via a loaded solid carrier material such as zeolite or starch. In this case the benefit agent usually exists as a liquid which is applied to the carrier material and is absorbed within the solid particle. A final approach is via core-shell particles, in which the benefit agent is a component of a liquid core which is surrounded by a solid shell. However, there are a number of problems encountered when using these known methods.
Loaded carrier materials suffer from two issues. The first is the ability to attach to the substrate. Attachment often relies upon attractive forces such as charge attraction between the solid carrier material and the substrate. If the surface has a charge that is similar to that of the carrier material outer surface then attachment is unlikely. Secondly, even if attachment to the substrate should be successful, movement of the benefit agent from the carrier material to the substrate can be problematic. This is because the solid carrier material is attached to the substrate, and so the liquid absorbed into the carrier material may not be able to easily transfer as it is not in direct contact with the substrate.
Liquid droplets overcome some of the disadvantages of loaded carrier materials. Firstly, since they are liquid, they can attach to the substrate without the same requirement as for solid particles, such as charge attraction, etc. Attachment is facilitated by liquid-solid attachment, i.e. ‘wetting’. Wetting’ is essentially the extent to which a liquid can wet a solid, and is a function of the force of adhesion between a liquid and a solid. This type of adhesion is evident, for example, when droplets of a liquid form on a solid surface, e.g. water droplets on glass. Furthermore, the ability of the benefit agent to reach the substrate surface will also be improved. This is because when the droplet adheres to the substrate, the benefit agent can easily pass through the liquid and directly to the substrate surface. However, liquid droplets tend to be spherical. This results in a low surface area for initial contact to the substrate, especially if the substrate presents a low surface area to the droplet itself, such as a natural fiber (examples being hair or cotton fiber) or a synthetic fiber (examples being nylon or polypropylene). Hence, initial attachment tends to be problematic.
Core-shell particles comprise a solid outer shell and a liquid inner core comprising the benefit agent. These types of particle are often spherical, but can also be non-spherical hence providing a higher surface area for improved initial attachment and adhesion. However core-shell particles still suffer from the charge-based adhesion problems and transfer of benefit agent as those of loaded carrier material particles. For either solid particles or core-shell particles the contact area between particle and substrate is limited because solids tend not to deform much upon contacting a substrate. This is especially problematic when the substrate has a non-planar surface topography, such as a curved hair or fibre.
Thus, there remains a need in the art for a benefit agent delivery particle that at least partially overcomes the above-mentioned problems.
It has now been surprisingly found that a non-spherical liquid droplet comprising a solid material that defines the shape of the droplet overcomes the above-mentioned problems. The solid material allows the droplet to have a non-spherical shape, but since the droplet is liquid over its entire surface, optimal attachment to the substrate can be achieved due to the wetting of the substrate and spreading onto the substrate by the liquid droplet.